A typical wireless communication system comprises a plurality of wireless communications devices exchanging data with each other. In some wireless communication systems, for example, infrastructure networks, the system may further comprise a wireless base station for managing communications between the wireless communications devices. In other words, each intra-system communication would be exchanged via the wireless base station. In other wireless communication systems, for example, mesh networks and ad hoc wireless networks, the wireless base station may be omitted, i.e. the wireless communications devices may communicate directly with each other.
One form of interference that the wireless communications device may encounter is multipath interference. Multipath interference occurs when multiple signals of the same transmission arrive at the receiver wireless communications device, each signal traveling via a different path. The typical causes of multipath interference include, for example, atmospheric ducting, ionospheric reflection and refraction, and reflection from water bodies and terrestrial objects, such as mountains and buildings.
More specifically, when two wireless communications devices communicate over hilly terrain, the resulting multipath interference may be problematic. In some applications, for example, voice communications, the multipath interference may prevent successful communications.
One approach to a wireless communication system is the OpenSky communication system, as available from the Harris. Corporation of Melbourne, Fla., the assignee of the present application. In particular, the OpenSky wireless communication system may provide digital voice transport to radio communications applications and devices, i.e. handsets. As will be appreciated by those skilled in the art, the OpenSky communication system uses a Reed Solomon (RS) code to protect time division multiple access (TDMA) slots or bursts. In fading multipath applications, for example, the hilly terrain (HT) channel (two fading paths 13 μs apart with each path having a 40 Hz Doppler spread and where the power of the second path is 8.6 dB lower than the first path), the OpenSky communication system may suffer from block error rates that prevent successful digital voice communications.
An approach to mitigating multipath effects in a code division multiple access (CDMA) spread spectrum wireless communication system is disclosed in U.S. Pat. No. 5,654,979 to Levin et al. In this approach, the receiver device includes a plurality of parallel demodulators that track respective multipath signals. Each demodulator applies the same algorithm to each multipath element found and then combines all the demodulated results into one result prior to decoding. The receiver device searches for the most powerful multipath signals and assigns demodulators based upon a stored algorithm. In other words, this approach simply applies a standard rake receiver in a parallel manner.